Yeah, it kind of sucks, but think about it as: You work for the charity, they pay you, then you donate the money you were paid back to the charity. The pay and the donation cancel each other, and it works the same way when the pay and the donation are both zero dollars.
Actually, that's not a bad idea. Start-ups that value patent reform could band together and give a few hours a month to doing this, and I'll bet it would make a pretty significant dent.